(i) Field to which the invention relates
The present invention is with respect to a dressing apparatus for the cup-type abrasive wheel of a machine for the part-generating or part-form grinding of spiral bevel gearwheels, the abrasive wheel having concave and convex grinding flanks in a groove (or on a ridge), the apparatus having a diamond dressing tool supported on a dressing tool head by way of which it may be rocked and on each motion may be moved in relation to each of the grinding flanks of the abrasive wheel.
(ii) The prior art
Within the framework of the present invention, spiral bevel gearwheels may be taken to be bevel gearwheels with circular pitch curves and other forms of spiral bevel gears. Such bevel gears may undergo grinding in a part-generating process using cut-type abrasive wheels working within the tooth spaces of the bevel gearwheel and acting on two tooth flanks at the same time so that the abrasive wheel will have two straight-flanked conical grinding faces or flanks taking the form of the two sides of an outer cone ring, running out from a plane normal to the axis of turning of the abrasive wheel. Such a grinding process is generally known in the art. In an earlier suggestion (see U.S. application Ser. No. 904,883), the grinding of the two sides or flanks of a given tooth, was to be undertaken using cup-type grinding or abrasive wheels, whose two grinding flanks are turned towards each other, forming between them a cone groove in a plane normal to the axis of grinding. Such a system makes possible the exact grinding not only of a bevel gearwheel, but furthermore the counter-wheel to be used with it, in one and the same working step.
However, in each of these two systems, there is the question of dressing the cup-type abrasive wheel. In an earlier form of apparatus of the sort noted (see U.S. Pat. No. 1,609,947) such dressing is caused by advancing the dressing tool for each grinding flank of the cup-type abrasive wheel. The dressing tool, in the form of a single diamond, is guided along a straight line at the outline of the working flanks of the abrasive wheel using a lead-screw. The change-over or transfer between these two motions is undertaken in such a way that the dressing tool head is rocked through 180.degree. about a rock axis, which is generally parallel to the axis of the abrasive wheel. By having the lead-screw at an angle to the rock axis, it is possible to make certain that the lead-screw is parallel to the generatrix of the working flank of the abrasive wheel in question without any further adjustment being necessary. This is naturally only possible for a given angle included between the work or grinding flanks of the abrasive wheel.
In this prior art apparatus of the sort noted in the first place, it has turned out to be a shortcoming that dressing or truing is a generally slow operation and so high in price. Furthermore, although the dressing tool head is generally simple in design, this is responsible for the shortcoming that no adjustment for use with cup-type abrasive wheels with different included angles between the working flanks is possible. Lastly, it is, generally speaking, not possible with this old system to undertake dressing of abrasive wheels in which the working or grinding flanks are the two sides of a double conical groove. Much the same is furthermore true for a further apparatus on the same lines known in the art, in the case of which a number of single diamonds are moved along the outline or profile of the cup-type abrasive wheel, each on its own diamond support head.
Furthermore, a different design of dressing apparatus has been put forward (see German Auslegeschrift specification No. 2,327,846, which corresponds to U.S. Pat. No. 3,855,992) which is to be used for dressing an abrasive wheel designed, for example, for working the race rings of ball bearings or the like, that is to say workpieces which, generally speaking, have a circular cross-section groove with cylindrical faces to its two sides. This prior art dressing system, which is different from the family of apparatus forming the starting point of the present invention, makes use of a dressing or truing roller which, on dressing, is rocked so as to be at an angle to the axis of turning of the abrasive wheel to be trued and the axis of symmetry of the dressing roller. When the particular part of the tool outline is being dressed, there is point contact between the abrasive wheel and the dressing roller, while in the end positions of the dressing roller there is line contact with the cylindrical parts of the abrasive wheel. So far, this prior art apparatus has not been responsible for any further development of dressing apparatus of the sort noted in the first place. Moreover, the simple use as such of the dressing roller of this known apparatus in the case of the dressing of cup-type abrasive wheels of the sort noted in the first place would not be responsible for the best, high quality work because, in this respect, the different curvature conditions of the grinding flanks to be dressed would not be taken into account.